Transport in Plants

As living organisms, plants need a system to transport minerals such as ions, food and water around. Transportation in plants is carried out by two different tubes:

  • Xylem
  • Phloem

Xylem vessels move water and mineral ions from the roots to the leaves. Food substances such as sucrose and amino acids are mainly transported by phloem vessels from the leaves to the rest of the plant.

  • So, the veins in a leaf are made from xylem tubes transporting water to the leaf and phloem tubes transporting sugars away from it.

The diagram below shows the process of water and mineral ions taken up by plants.

  • The process that transports substances in the xylem is called transpiration
  • The process that transports substances in the phloem is called translocation

Root Hair Cells

Root hair cells have a small thin extension. It pokes out into the soil to absorb water by osmosis. The purpose of these root hair cells is to increase the surface area of the root that is in contact with the soil. This allows the plant to absorb more water and minerals.

They also contain a lot of mitochondria, which release energy from glucose during respiration. This provides the energy needed for the active transport of mineral ions.

  • As root cells are underground, where it is dark, they do not have chloroplasts.

The diagram below shows the absorption of water and minerals from the soil by root hair cells.

Water passes into the root hair cells by osmosis due to the higher water potential of the soil compared to the cytoplasm of the root hair cell. Once the water is absorbed by the plant through the root, it is transported by the xylem to the leaves, entering the mesophyll cells.

The water absorbed by the soil is used for:

  • Photosynthesis
  • Supporting leaves by keeping the cells rigid
  • Cooling the leaves by evaporation
  • Transporting dissolved minerals around the plant